Several types of test devices have been or are employed for the purpose of evaluating the crack detecting efficiency of fluorescent penetrants. The objective of the devices is the simulation of the finer and more difficult to detect forms of flaws or cracks in metals. Included among the devices are chromium plated crack plates, brittle iron plated crack plates, quench-cracked aluminum blocks, cracked ceramic blocks, metal bars with fatigue cracks, metal sleeves bolted together under compression, and a laboratory meniscus lens apparatus for measuring the thinnest film at which a penetrant shows fluorescence upon exposure to ultraviolet light. Of these devices, the chromium plated crack plates are probably the most useful for simulating very fine cracks. However, these crack plates are not entirely satisfactory because they are quite expensive and the crack widths are not reproducible.
It is an object of this invention, therefore, to provide an improved, low cost, test device which can be mass produced to reproducible standards of "crack" widths ranging from moderately fine to coarse.
Another object of the invention is to provide a method for determining the efficacy of visible dye or fluorescent penetrants in detecting flaws or defects in objects such as aircraft structural panels, machine parts, jet engine components, and the like.
A further object of the invention is to provide a method of comparing the efficiency of two or more penetrants in detecting flaws or defects in objects.